During the last fifteen years, however, our knowledge of the works of art executed by these ancient men has increased to an extraordinary extent, chiefly owing to the energy and skill of the French explorers of the caverns in the south central region of that country. As long ago as 1879 a little girl, the daughter of Señor Sautuolo–a proud woman she should be if alive to-day–when visiting the cavern of Altamira, near Santander, in the north of Spain, with her father, drew his attention to a number of "pictures of animals," painted on the rocky vault or roof of the cave. At first no one believed that these pictures were more than a few hundred years old, whilst some held them to be modern and made with fraudulent purpose. In 1887 Piette, the distinguished French investigator of the remains of human work in the caverns of the French Pyrénées (whose great illustrated book of carved and engraved portions of reindeer antler, ivory, and stones discovered by his excavations, is a classic), declared that in his opinion the pictures of the Altamira cave were of the same age as the bone and ivory carvings of the Madeleine cave–that is to say, dated from what "prehistorians" call the later Palæolithic age, an age when the mammoth, the bison, the cave lion, and the reindeer still existed in Western Europe, and when the British Isles were not yet separated by sea from the Continent. The age indicated is probably from 25,000 to 50,000 years ago. Still, the opinion prevailed that the "wall-drawings" and "roof-drawing" of the Altamira cave were either mediæval or modern until the French explorers discovered wall-paintings in some of the caves of the Dordogne. Then they proceeded to a careful investigation of the Altamira cave, and discovered conclusive evidence of the great age of the paintings by the removal of some of the undisturbed deposit in the cave, in which were found flint implements and small engravings on bone, proving the deposit to be of the late Palæolithic age. When this deposit was removed, pictures of animals, partly engraved and partly completed in colour (black, red, yellow, and white), were found on the wall of the cave previously covered up by the deposit. M. Cartailhac, who had been a leading opponent of the view that the Altamira wall-pictures were very ancient, now renounced his former position and became an enthusiastic investigator and exponent of these pictures. M. Breuil, who had discovered wall-pictures, including those of the mammoth, in French caves, and had been met by disbelief and even suspicion, now received due recognition, and joined Cartailhac in preparing a complete account of the wall and roof pictures of the Altamira cave. The Prince of Monaco, who had carried out, with the aid of French experts, an investigation of the caves on his property at Mentone, on the Mediterranean "Riviera," undertook the expense of producing a splendid volume, giving coloured reproductions of the Altamira pictures.